This one is hard to describe because we can't reliably reproduce it. However, a couple of us have seen where our dedicated server for Valley sees certain players get disconnected, then when they reconnect, they continue to be disconnected.
I noticed on my own server that the person in question had two things that could be suspect:
1. He is on Comcast xfinity and I am on Comcast xfinity, within 10 miles of each other. Not sure if this would make a difference as far as the networking goes...
2. On the ManiaPlanet Player Page, list of Favorite Servers, the player in question continued to show as connected to my server even though he was disconnected. The game client, when looking at the scores list did NOT show the disconnected player, and XAseco2 would continue to send chat messages when the player would connect/disconnect.
No other players on my server were experiencing the problem (that they reported) -- and I didn't notice any other "ghosted" players that were disconnected, but still listed on the player page.
My server set up (killer606, please log your specs here too...)
OS: Windows XP Professional
Internet: Comcast xfinity 50Mbit / 10Mbit (down/up)
ManiaPlanet Server: 2013-07-04a (with hotfixed Valley pack)
Server Controller: XAseco2 with TMKarma, Records Eyepiece and Dedimania plugins running.
I don't know if Canyon and Stadium are having this problem too, as I have been playing Valley all weekend. I will be happy to test those if I can pull people away from Valley (good luck with that!!

I want this thread here so we can start building more accurate information as it unfolds.